I have a spreadsheet with copious amounts of data (10 sheets
with ~80 columns x 8000 rows). The file size is so large that
I need to break the data into groups and then delete the rows
that do not pertain.

I have identified the rows I would like to delete by writing a
formula in Column A. This formula returns the word "DELETE"
for the rows I want to delete.

Since you already have formulas in place in Column A displaying either the
word DELETE or the empty string, then give this macro a try...

Sub DeleteDELETEs()
Dim UnusedCol As Long, LastRow As Long, Cell As Range, WS As Worksheet
Const WSnames As String = "Sheet1,Sheet2,Sheet3,Sheet4,Sheet5"
Application.ScreenUpdating = False
Application.Calculation = xlCalculationManual
On Error Resume Next
For Each WS In Worksheets(Split(WSnames, ","))
UnusedCol = WS.Cells.Find(What:="*", SearchOrder:=xlByColumns, _
SearchDirection:=xlPrevious, LookIn:=xlFormulas).Column + 1
LastRow = WS.Cells.Find(What:="*", SearchOrder:=xlRows, _
SearchDirection:=xlPrevious, LookIn:=xlFormulas).Row
With WS.Range(WS.Cells(1, UnusedCol), WS.Cells(LastRow, UnusedCol))
.Value = WS.Range(WS.Cells(1, "A"), WS.Cells(LastRow, "A")).Value
.SpecialCells(xlCellTypeConstants).EntireRow.Delet e
End With
Next
On Error GoTo 0
Application.Calculation = xlCalculationAutomatic
Application.ScreenUpdating = True
End Sub

The only thing you need to do is change the cells being assigned to the
WSnames constant (the Const statement) to the names of the sheets you want
to run the code against. NOTE... do NOT put any spaces around the commas in
the list you create for this assignment.

Rick Rothstein (MVP - Excel)